In the realm brush type motor drives, there exists a need to detect whether or not a locked rotor condition exists in order to prevent the occurrence of thermal events. There exist many possible means of achieving this, including variable reluctance coils placed between the magnets in the stator, Hall effect sensors used to detect shaft rotation, as well as the use of current sensors. However, the use of discrete feedback sensors in the motor may adversely affect the size, cost, complexity, power consumption and, particularly with Hall effect sensors, reliability of the motor.
Thus, there is a need to detect armature rotation and/or current in a brush type DC motor by using existing components within the motor, with minor modifications, as an armature rotation sensor.